1997 200hp johnson too much prop?

[fowlerprowler]

Hello, I just purchased a 1998 Triton SF21 fish and ski with a 1997 Johnson Venom 200 hp outboard, it has a 4 blade SS OMC Renegade 13.5 x 27 pitch prop on it. the motor turns at 4600 RPMs and runs 58 mph (by water pressure speedometer). Sounds like thats too much prop for the motor since the RPM's are so low, right? The boat has a great hole shot but the low RPM's bugs me. I know the venom's have had issues but don't ya'll think it would be ok to try a different prop to get the RPM's up? If so, which size would you recommend? and what would be the max RPM's to try to get? Thanks in advance.

 

[steelespike]

Re: 1997 200hp johnson too much prop?

While a 27" pitch could be on the high side It would appear to me that If too much prop
you wouldn't have a "great hole shot" Also I wonder if 4600 would produce 58 mph.
You may want to verify your tach is accurate.
My info indicates your motors max rpm is 6,000.You would need about a 7" pitch change to get to 6,000.20" isn't excessively small based on some other 200hp setups I looked at.
If you varify your tach then a pitch change would be in order.Try to stick with the same brand and model prop for more predictable results.

 

[fowlerprowler]

Re: 1997 200hp johnson too much prop?

thanks for the info. I was curious about the rpm's vrs the mph too, but don't know the gear ratio of the motor to see if that pitch at the rpm's would produce that speed. Is there a tool or something to test the tach with? I'd hate to buy a new tach just to see if the old one is accurate. As far as the hole shot, I said great hole shot meaning it does jump on plane fast. The nose of the boat is only in the air for a few seconds before it's on plane which could be because of the weight forward of the fish and ski. The only sluggishness of it that I can tell is that it takes longer (not alot, just noticable to me)to get to top speed than the other bass boats I've owned but I figured that was because it's a heavier boat than most. Could the prop cause that?

 

[steelespike]

Re: 1997 200hp johnson too much prop?

Your gear ratio is 1.86.Math in my head (dangerous)it seems 4600 might produce about 60 mph.
Using round figures and disregarding slip.
Largest prop listed here is 28" So your basically at the top of the list and I would think acceleration from on plane to top speed might be a little slower than typical.
And a 20" prop doesn't seem too extreme by my research.

 

[fowlerprowler]

Re: 1997 200hp johnson too much prop?

update: I tried a 14.5 x 24 3 blade ballistic with these results. With just me in the boat, it cavitated when I tried to take off and I had to ease into it until it got on plane then it would turn it at 5100 RPM's and GPS's at 58 mph. When my buddy got in the boat (200 lbs), it wouldn't get on plane. It would just cavitate no matter how easy I tried to ease into it. We never took off. Only thing with the prop was it looked like someone had drilled the holes out on the side larger than what they should be (1/2" holes). Probably not a good test but finding props to try isn't real easy.

I put the 27 pitch back on it and with both of us in the boat, no problems taking off. It maxed out at 4600 RPMs and GPS'd at 56-57 mph. Again, on plane in a matter of seconds.

So here's the math:
5100 rpm x 24 ? 1.86 ? 1056 = 62.3 mph no slip (58 mph gps= 7% slip)(1 adult)
4600 rpm x 27 ? 1.86 ? 1056 = 63.2 mph no slip (57 mph gps= 10% slip)(2 adults)

are those legit sounding slip % for that boat? That's one big boat and 25 hp underrated. Sounds like a tach check may be in order? (kinda like you said at first) Will have to see if the local boat shop has a spare tach laying around I can test.

 

[fowlerprowler]

Re: 1997 200hp johnson too much prop?

update #2: put a 3 blade SS 14.5 x 24 raker on it saturday and ran it. Didn't have my GPS but speedometer showed 63-64 mph, the boat lifted better, and it got on plane even faster.....BUT the tach only showed 5000 RPM's. Had my GPS today, it GPS's 60 mph, speedometer showed 63-64 mph, same lift and same speed on plane as saturday EXCEPT the tach showed 5800 RPM's. My buddy got in and it still showed 5800 RPM's and GPS's at 58 mph.

Anyways, that's where I'm at. Very confident now that the tach was not reading accurately (who knows, may still not be) but just wanted to let you know how it's turned out and say thank you for your time and your help.

 

[Dr Bass]

Re: 1997 200hp johnson too much prop?

do you still have the 27 pitch prop? if so you wanna sell it?

 

[steelespike]

Re: 1997 200hp johnson too much prop?

Its highly unlikely he will be reading this old post.If you click on his name you can send a pm.
(private message)

 

[fowlerprowler]

Re: 1997 200hp johnson too much prop?

No I don't, I traded it for another prop but the guy I traded with may be looking to sell since he has it just as a back up. Not for sure, but I'll check.

 

[fowlerprowler]

Re: 1997 200hp johnson too much prop?

sent you a PM with his info, he would be willing to sell. thanks.